Previous experiments for carbon capture and storage (CCS) have involved injecting pure CO₂ into sandstone, or deep, salty aquifers (water-bearing rock layers). The fear is always that the CO₂ could find a way to leak back out into the atmosphere. A possible solution might be the Carbfix project.

In Iceland, Juerg Matter, Southampton University, UK, and colleagues, in cooperation with the Hellisheidi geothermal power plant outside Reykjavik, have pumped CO₂ and water underground into volcanic rock. Reactions with the minerals in the deep basalts convert the carbon dioxide to a stable, immobile chalky solid on the order of months. The low pH of 3.2 causes calcium and magnesium ions to dissolve in the basalts. They react with carbon dioxide to make calcium and magnesium carbonates. CO₂ tagged with carbon-14 proved that no CO₂ is leaking back to the surface.

The researchers think that in the future power plants could use this technology in places where there is a lot of basalt. However, the approach is quite expensive and there is a lot of water involved. Only around 5 % of the mass sent underground is CO₂. More experiments are needed to see how the approach works in different regions and with larger quantities of CO₂.

• The CarbFix Project, Reykjavik, Island
• Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions,
  J. M. Matter, M. Stute, S. O. Snaebjornsdottir, E. H. Oelkers, S. R. Gislason, E. S. Aradottir, B. Sigfusson, I. Gunnarsson, H. Sigurdardottir, E. Gunnlaugsson, G. Axelsson, H. A. Alfredsson, D. Wolff-Boenisch, K. Mesfin, D. F. d. l. R. Taya, J. Hall, K. Dideriksen, W. S. Broecker,
  Science 2016, 352, 1312–1314.
  DOI: 10.1126/science.aad8132